EP0467678B1 - Vorrichtung zur variablen Längenkodierung und Vorrichtung zur variablen Längendekodierung - Google Patents

Vorrichtung zur variablen Längenkodierung und Vorrichtung zur variablen Längendekodierung Download PDF

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Publication number
EP0467678B1
EP0467678B1 EP91306536A EP91306536A EP0467678B1 EP 0467678 B1 EP0467678 B1 EP 0467678B1 EP 91306536 A EP91306536 A EP 91306536A EP 91306536 A EP91306536 A EP 91306536A EP 0467678 B1 EP0467678 B1 EP 0467678B1
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Prior art keywords
state
variable length
transition
accordance
state transition
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French (fr)
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EP0467678A3 (en
EP0467678A2 (de
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Kenshi C/O Intellectual Property Div. Dachiku
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Toshiba Corp
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Toshiba Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
    • H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
    • H03M7/40—Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code
    • H03M7/42—Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code using table look-up for the coding or decoding process, e.g. using read-only memory

Definitions

  • the present invention relates to a variable length coding apparatus which variable-length-codes the audio, image, data, and other information signals and generates coded arrays and a variable length decoding apparatus which decodes variable length coded arrays.
  • Variable length coding is an encoding system to compress the information content by assigning a short code to the information of high occurrence probability and a long code to the information of low occurrence probability by the use of statistical properties which audio, image, data, and other information signals possess when these information signals are encoded.
  • the differences of adjacent pixels are concentrated to the vicinity of zero because the correlation between adjacent pixels is high. Therefore, assigning a pixel whose absolute value of the difference is small to a short code and that of large absolute value to a long code enables the compression of the information content.
  • the binary image such as facsimile data
  • encoding the white length and the black length (run-length coding) and assigning the run length with higher occurrence probability to a short code and that with lower occurrence probability to a long code enables the compression of the information content.
  • variable length coding apparatus which carries out coding with the code length made variable generally has a variable length ROM (read-only memory) which stores in advance a variable length code table listing the encoded information signal with correspondence to the variable length code, and a word length ROM, a shift register, and a word length counter.
  • a variable length ROM read-only memory
  • information signals comprising n-bit digital data are inputted to the first input terminal, while load pulses are inputted to the second input terminal.
  • the information data is converted to the variable length code and k-bit word length data by the variable length ROM and the word length ROM, and loaded into the shift register and the word length counter, respectively, by the load pulse.
  • the word length counter counts down with the digital value of the loaded word length data designated as an initial value and stops counting when the contents reduce to zero.
  • the output signal of the output terminal is "L,” indicating that the variable length coded data from the shift register will appear at the output terminal during this period.
  • variable length decoding apparatus which decodes the variable length codes generally has a shift register, ROM for storing the variable length codes with correspondence to decoded values, and a word length counter.
  • variable length coded array is inputted to the first input terminal and the reset pulse is inputted to the second terminal at the first timing of the variable length coded array.
  • the word length counter is reset with the reset pulse via a gate and every time one variable length coded array is inputted to the first input terminal, the word length counter counts up by the clock.
  • the variable length coded array is inputted to the shift register in series and shifted by 1 bit.
  • Thek-bit word length data outputted from the word length counter and the shifted variable length coded array are given to ROM.
  • the ROM stores the variable length code table which lists variable length codes with correspondence to decoded values, and if a coded array with the word length removed from the shift register output is located on the variable length code table, the ROM outputs the decoded value and the coincidence pulse VD of negative logic.
  • the coincidence pulse VD is latched with a latch and outputted from the output terminal.
  • the decoded value outputted from the ROM by the coincidence pulse is latched by a latch and outputted from the output terminal.
  • the coincidence pulse is supplied to the word length counter as well via gate and resets the word length counter.
  • variable length code tables stored in a ROM and a large storage capacity ROM is needed, creating a problem that the circuit scale is extremely large.
  • the objective of this invention is to provide a variable length coding apparatus and a variable length decoding apparatus which can be realised with smaller-scale hardware than the conventional.
  • the variable length coding apparatus of the present invention comprises state holding means for holding a current state of input data; state transition means for outputting data representing a next state to be transited and data in accordance with a predetermined transition in state and in correspondence with the current state held by the state holding means; means for inputting a state corresponding to a to-be-coded information signal to the state holding means every time a to-be-coded information signal is inputted; and means to feed back to the state holding means the state outputted from the state transition means, wherein the state transition means outputs a variable length code corresponding to the to-be-coded information signal as said data every time the next state is transited.
  • variable length code table to be used next is selected from the multiple number of variable length code tables and the state transition means outputs the next transition state and one-bit data in accordance with the predetermined state transition with respect to the variable length table selected as above in response to the current state of the state holding means.
  • variable length decoding apparatus of the present invention comprises state holding means for holding a current state of input data; state transition means for shifting the state being held by the state holding means to another state in accordance with a predetermined transition in state every time one-bit data of a to-be-decoded variable length code is inputted thereto; means for setting the state holding means at a specified state at every breakpoint of the to-be-decoded variable length code; and means for feeding back, when a specified state is outputted from the state transition means, the state from the state transition means to the state holding means, wherein the state transition means outputs a state obtained at the breakpoint as a decoded value corresponding to the variable length code every time there is a transition in state.
  • variable length decoding apparatus which decodes the variable length codes encoded by using a multiple number of variable length coding tables
  • the variable length coding table used for coding is determined from the multiple number of the variable length coding tables, and the state transition means outputs a next transition state and a delimiter signal in accordance with the predetermined state transition with respect to the variable length table determined as above in response to the current state of the state holding means.
  • designing the apparatus to output the variable length code or its decoded value by the use of state transition requires only the address inputs equivalent to the total number of the states when a ROM is used for the state transition circuit, thereby greatly reducing the ROM capacity as compared to the conventional apparatus which stores the variable length code tables in ROM.
  • ROM may have only 9 bits for the address input and 11 bits for the output (including variable length coded output and indication signals).
  • the decoding apparatus if the maximum coding length of the to-be-decoded variable length code is 20-bit data and the total of the information signal values is 256, only about 512 signal values are required for the total of the states and the 512 x 9 bits are suffice for the ROM capacity.
  • the state transition circuit can be realized by the combinational logic circuit.
  • the variable length coding apparatus comprises a selector 13, a register 14 for holding the state, and ROM 15 for shifting the state.
  • the to-be-coded information signals are inputted, while to the input terminal 12, the load pulse LD is inputted.
  • the selector 13 is operated by clock and selects the information signal inputted to the input terminal 11 while the load pulse LD is given, and except the period, the selector selects the state signal outputted from ROM 15.
  • the register 14 holds the signal selected by the selector 13 as a state signal.
  • ROM 15 has, for example, 4 bits for the address input and 6 bits for output, and using the state signal held in the register 14 as an address input, it outputs the to-be-shifted next state signal as lower 4-bit data as well as outputting the coded bit showing the variable length code to the output terminal, and outputs the 1-bit output signal VD showing the period when the variable length code is effectively outputted from the output terminal 16 as the code bit.
  • Fig. 2 is an example of a variable length coding table prepared by using the Huffman encoding method, in which the information signal is encoded in accordance with the probability of occurrence, that is, the frequently occurring information signal is encoded with a short bit length and the information signal is encoded with a longer bit length as the occurrence rate decreases
  • Fig. 3 shows a state transition diagram to encode in accordance with the code table of Fig. 2
  • Fig. 4 shows the contents of ROM 15 based on the state transition diagram of Fig. 3.
  • Fig. 5 shows a timing chart when the information signal called "0123" to the input terminal 11. However, the information signal (input value) is expressed with the 4-bit parallel digital data, for example.
  • the information signal is selected by the selector 13 in response to the load pulse LD and "0" is held at the register 14 as the current state signal. With this, the address input of ROM 15 becomes “0".
  • "1" is outputted to the output terminal 16 from ROM 15 as a code bit indicating the variable length code and at the same time the output signal VD to the output terminal 17 becomes "0", which indicates that the code bit is effective.
  • "15” is outputted from ROM 15 as the state signal following "0", and is fed back to the register 14 via the selector 13 before the next value of the information signal is inputted.
  • the next value "1" of the information signal is inputted to the input terminal 11 and held at the register 14 via the selector 13.
  • the address input of ROM 15 becomes “1” and first of all "0” is outputted as a code bit indicating the variable length code to the output terminal 16 from ROM 15 and at the same time the output terminal 16 from ROM 15 and at the same time the output signal VD becomes "0", and "0" is outputted as the state signal following "1".
  • This state signal "0" is fed back to the register 14 via the selector 13 and "1" is outputted to the output terminal 16 from ROM 15 as a variable length code and the output signal VD becomes "0".
  • This state signal "7” is fed back to the register 14 via the selector 13 to bring the address input of ROM 15 to be “7”, and "0” is outputted to the output terminal 16 as a variable length code from ROM 15 as well as bringing the output signal VD to be “0".
  • "8" is outputted as the state signal following "7”.
  • This state signal "8” is fed back to the register 14 via the selector 13 to bring the address input of ROM 15 to be “8”, and "0” is outputted to the output terminal 16 as a variable length code from ROM 15 as well as bringing the output signal VD to be “0".
  • "15” is outputted as the state signal following "8".
  • This state signal "15” is fed back to the register 14 via the selector 13 to bring the output signal VD to be "1", indicating that the variable length encoding for the next value of the information signal is completed. That is, the variable length code output in this event is "0000.”
  • variable-length-encoding is carried out in accordance with the state transition diagram shown in Fig. 3 and the table in Fig. 4.
  • Fig. 6 is the other embodiment of the variable length coding apparatus related to the present invention, in which a combinational logical circuit 21 combining AND, OR gate, inverter, etc. is used in place of ROM 15 of Fig. 1.
  • the register 22 corresponds to the register 14 in Fig. 1 and because the combinational logical circuit 21 has functions of the selector 13 in Fig. 1 in this event, the register 22 is directly inserted between the state signal input and the output of the combinational logical circuit 21. That is, the combinational logical circuit 21 logically process the input signal in accordance with the logical expression shown in Fig. 7. In the logical expression of Fig.
  • Fig. 8 shows another embodiment of a variable length coding apparatus related to the present invention, which uses multiple number of variable length code tables.
  • two combinational logical circuits 33 and 34 are used.
  • the first combinational logical circuit 33 decides which variable length code table to be used, is reset to the initial state by the reset signal to be inputted to the input terminal 31, and determines the initial table number from the multiple number of variable length code tables to output.
  • the second combinational logical circuit 34 is configured in accordance with the logical expression corresponding to the state transition predetermined on the basis of each of the multiple number of variable length code tables, and the basic functions are same as those of ROM 15 of Fig. 1 or of the combinational logical circuit 21 of Fig. 6, and carries out the variable length coding in accordance with the state transition diagram corresponding to the variable length coding table decided by the first combination logical circuit 33.
  • the first combinational logical circuit 33 is given conditions to determine which information signal is to be encoded next from the input terminal 32 and outputs the table No. in accordance with the specified rule.
  • variable length decoding apparatus is described.
  • Fig. 9 is a block diagram showing one embodiment of the variable length decoding apparatus related to the present invention.
  • This variable length decoding apparatus comprises a gate circuit 43, a selector 44, a register 45 as a state holding circuit, ROM 46 as a state transition circuit, and registers 47 and 48.
  • the selector 44 is given the output of the gate 43 as a select signal SEL and selects either one of the signal corresponding to the state "15" (digital data) or the state signal outputted from ROM 46.
  • the register 45 is operated by the clock and holds the signal selected at the selector 44 as a state signal.
  • ROM 46 outputs the next state signal as the lower 4 bits by giving the bits of the variable length code inputted into the input terminal 41 to the address input MSB (most significant bit) and the state signal held in the register 45 to the lower 4 bits of the address input and then outputs the signal showing the breakpoint of the variable length code as MSB.
  • the register 47 holds the lower 4-bit output of ROM 46 by the clock and outputs the decoded signal to the output terminal 49.
  • the register 50 holds the MSB output of ROM 46 with the clock and provides to the output terminal 50 from the output terminal 49 with the output signal VD indicating the period when the decoded value is outputted.
  • variable input length codes are those shown in Fig. 2.
  • Fig. 10 is a state transition diagram for variable-length-decoding
  • Fig. 11 is a drawing showing an I/O relationship of the ROM 15 storing the variable length decode table based on the state transition diagram of Fig. 3.
  • Fig. 12 is a timing chart when a sequence of variable length codes "101000000010010" is inputted to the input terminal 41.
  • variable-length-decoding is carried out in accordance with the state transition diagram shown in Fig. 10.
  • Fig. 13 is the other embodiment related to the present invention showing a variable length decoding apparatus, in which a combinational logical circuit 51 combining AND, OR gate, inverter, etc. is used in place of ROM 46 of Fig. 9.
  • the register 52 corresponds to the register 45 in Fig. 9 and because the combinational logical circuit 51 has functions of the selector 45 in Fig. 9 in this event, the register 52 is directly inserted between the input and the output of the state signal of the combinational logical circuit 51.
  • Fig. 14 is an example of the logical expression of the combinational logical circuit 51 in Fig. 13, indicating the case in which the state transition diagram of Fig. 10 is implemented.
  • Fig. 15 shows another embodiment of a variable length decoding apparatus related to the present invention, which uses multiple number of variable length code tables.
  • two combinational logical circuits 61 and 62 are used.
  • the first combinational logical circuit 61 is reset to the initial state by the reset signal inputted to the input terminal 42 and decides the initial table number from the multiple number of the variable length code tables and outputs the result to the output terminal 65 via the registers 63 and 64.
  • the second combinational logical circuit 62 is configured in accordance with the logical expression corresponding to the state transition predetermined on the basis of each one of the multiple number of variable length code tables, and the basic functions are same as those of ROM 46 of Fig. 8 or of the combinational logical circuit 51 of Fig. 13, and carries out the variable length decoding in accordance with the state transition diagram corresponding to the variable length code table decided by the first combinational logical circuit 61.
  • the first combinational logical circuit 61 is given conditions to determine which information signal outputs the table No. in accordance with the rule specified by the decoded value.
  • variable length coding apparatus configuring in such a manner to determine the variable length code and its decoded value by using the state transition circuit has enabled the realization of variable length coding apparatus and variable length decoding apparatus using a ROM with a far smaller storage capacity than that of conventional apparatus.

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Claims (13)

  1. Vorrichtung zur Kodierung in variabler Länge, die folgende Komponenten umfaßt:
    ein Zustands-Haltemittel (14) zum Halten eines gegenwärtigen Zustandes von Eingangsdaten;
    ein Zustands-Umwandlungsmittel (15) zur Ausgabe von Daten, die einen nächsten zu durchlaufenden Zustand darstellen, und von Daten in Übereinstimmung mit einer festgelegten Umwandlung im Zustand und in Übereinstimmung mit dem gegenwärtigen Zustand, der durch das Zustands-Haltemittel (14) gehalten wird;
    ein Mittel (13) zur Eingabe eines Zustands, der einem zu kodierenden Informationssignal entspricht, in das Zustands-Haltemittel, jedesmal dann, wenn ein zu kodierendes Informationssignal eingegeben wird; und
    ein Mittel zur Rückkopplung des Zustands, der vom Zustands-Umwandlungsmittel (15) ausgegeben wird, in das Zustands-Haltemittel, bei der das Zustands-Umwandlungsmittel (15) einen Kode von variabler Länge ausgibt, der dem zu kodierenden Informationssignal als den genannten Daten entspricht, jedesmal dann, wenn der nächste Zustand durchlaufen wird.
  2. Vorrichtung zur Kodierung in variabler Länge nach Anspruch 1, bei der das Zustands-Umwandlungsmittel einen Speicher zur Speicherung einer Umwandlungstabelle umfaßt, die Kodes von variabler Länge entspricht, die das Informationssignal entsprechend der Wahrscheinlichkeit seines Auftretens speichert.
  3. Vorrichtung zur Kodierung in variabler Länge nach Anspruch 1, bei der das Zustands-Umwandlungsmittel einen Speicher (15) umfaßt, in dem eine Umwandlungstabelle gespeichert ist, die Kodes von variabler Länge entspricht, die ein häufig auftretendes Informationssignal mit einer kurzen Bit-Länge kodiert und die ein Informationssignal mit einer größeren Bit-Länge kodiert, wenn sich die Wahrscheinlichkeit des Auftretens des Informationssignals verringert.
  4. Vorrichtung zur Kodierung in variabler Länge nach Anspruch 1, bei der das Zustands-Umwandlungsmittel einen Logik-Schaltkreis (21) umfaßt, der in Übereinstimmung mit einem logischen Ausdruck konstruiert ist, der einer Umwandlung im Zustand entspricht.
  5. Vorrichtung zur Kodierung in variabler Länge nach Anspruch 1, dadurch gekennzeichnet, daß das Zustands-Umwandlungsmittel (15) folgende Komponenten einschließt:
       ein Zustands-Umwandlungsmittel (34), das eine Vielzahl von Tabellen von Kodes von variabler Länge hat, die in Übereinstimmung mit einer Vielzahl von zu kodierenden Informationssignalen und einer Vielzahl von Kodes von variabler Länge erstellt worden sind, und ein Tabellen-Bestimmungsmittel (33) zur Bestimmung einer als nächster zu nutzenden Tabelle mit Kodes von variabler Länge aus einer Vielzahl von Tabellen von Kodes von variabler Länge, wobei das Zustands-Umwandlungsmittel (34) einen nächsten Umwandlungszustand und Daten in Übereinstimmung mit einer Umwandlung ausgibt, die im voraus durch jede der Tabellen von Kodes von variabler Länge bestimmt wird, die durch das Tabellen-Bestimmungsmittel (33) in Übereinstimmung mit dem gegenwärtigen Zustand bestimmt worden ist, der durch das Zustands-Haltemittel (36) gehalten wird.
  6. Vorrichtung zur Kodierung in variabler Länge nach Anspruch 5, bei der das Zustands-Umwandlungsmittel (34) einen Logik-Schaltkreis umfaßt, der in Übereinstimmung mit einem logischen Ausdruck geschaffen wird, der einer Umwandlung im Zustand entspricht, die im voraus in Übereinstimmung mit jeder der Tabellen von Kodes von variabler Länge bestimmt worden ist.
  7. Vorrichtung zur Kodierung in variabler Länge nach Anspruch 5, bei der das Tabellen-Bestimmungsmittel (33) ein Mittel umfaßt, um in einen Anfangszustand zurückgestellt zu werden und eine Anfangstabellen-Nummer für die Auswahl einer der Tabellen von Kodes von variabler Länge zu bestimmen.
  8. Vorrichtung zur Kodierung in variabler Länge nach Anspruch 1, dadurch gekennzeichnet, daß das Zustands-Umwandlungsmittel einen Logik-Schaltkreis umfaßt, der in Übereinstimmung mit einem logischen Ausdruck geschaffen wird, der dem Informationssignal als den genannten Daten entspricht, jedesmal dann, wenn eine Umwandlung im Zustand erfolgt.
  9. Vorrichtung zur Dekodierung von variablen Längen, die folgende Komponenten umfaßt:
    ein Zustands-Haltemittel (45) zum Halten eines gegenwärtigen Zustands von Eingangsdaten;
    ein Zustands-Umwandlungsmittel (46) zur Verschiebung des Zustands, der durch das Zustands-Haltemittel (45) gehalten wird, in einen anderen Zustand in Übereinstimmung mit einer festgelegten Umwandlung im Zustand, jedesmal dann, wenn in dieses Ein-Bit-Daten eines zu dekodierenden Kodes von variabler Länge eingegeben werden;
    ein Mittel (44), um das Zustands-Haltemittel an jeder Bruchstelle des zu dekodierenden Kodes von variabler Länge in einen festgelegten Zustand zu setzen; und
    ein Mittel zur Rückkopplung eines Zustands vom Zustands-Umwandlungsmittel zum Zustands-Haltemittel (45), wenn ein festgelegter Zustand vom Zustands-Umwandlungsmittel (46) ausgegeben wird, bei der das Zustands-Umwandlungsmittel einen Zustand ausgibt, der an der Bruchstelle als ein dekodierter Wert ermittelt wird, der dem Kode von variabler Länge entspricht, jedesmal dann, wenn eine Umwandlung im Zustand erfolgt.
  10. Vorrichtung zur Dekodierung von variablen Längen nach Anspruch 9, bei der das Zustands-Umwandlungsmittel (46) einen Speicher zur Speicherung einer Dekodierungstabelle von variabler Länge umfaßt, die mit der Zustandsumwandlung für die Dekodierung übereinstimmt.
  11. Vorrichtung zur Dekodierung von variablen Längen nach Anspruch 9, bei der das Zustands-Umwandlungsmittel (46) einen Logik-Schaltkreis (51) umfaßt, der in Übereinstimmung mit einem logischen Ausdruck konstruiert ist, welcher der Zustandsumwandlung entspricht.
  12. Vorrichtung zur Dekodierung von variablen Längen nach Anspruch 9, dadurch gekennzeichnet, daß das Zustands-Umwandlungsmittel (46) folgende Komponenten einschließt:
    ein Tabellen-Bestimmungsmittel (61) zur Bestimmung einer zum Kodieren genutzten Tabelle von Kodes von variabler Länger aus einer Vielzahl von Tabellen von Kodes von variabler Länge, bei der eine Vielzahl von Kodes von variabler Länge einer Vielzahl von dekodierten Werten entspricht; und
    ein Zustands-Umwandlungsmittel (62), das eine Vielzahl von Tabellen hat, um einen als nächsten zu durchlaufenden Zustand und Daten in Übereinstimmung mit einer Zustandsumwandlung auszugeben, die im voraus in Übereinstimmung mit der Tabelle von Kodes von variabler Länge bestimmt worden sind, die durch das Tabellen-Bestimmungsmittel (61) bestimmt worden ist, und in Übereinstimmung mit dem gegenwärtigen Zustand des Zustands-Haltemittels.
  13. Vorrichtung zur Dekodierung von variablen Längen nach Anspruch 9, dadurch gekennzeichnet, daß das Zustands-Haltemittel ein Zustands-Haltemittel zum Halten eines ersten Zustands einschließt;
    das Zustands-Haltemittel (46) ein Mittel zur Bestimmung eines zweiten Zustands, der auf den ersten Zustand folgt, auf Grund des ersten Zustands, der durch das Zustands-Haltemittel gehalten wird, und der Eingangsdaten einschließt; und
    das Einstellmittel (44) ein Mittel einschließt, um das Zustands-Haltemittel (45) an jeder Bruchstelle in den Anfangszustand zu setzen, bei dem die Dekodierung des zu dekodierenden Kodes von variabler Länge abgeschlossen ist.
EP91306536A 1990-07-18 1991-07-18 Vorrichtung zur variablen Längenkodierung und Vorrichtung zur variablen Längendekodierung Expired - Lifetime EP0467678B1 (de)

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JP190062/90 1990-07-18
JP2190062A JPH0479421A (ja) 1990-07-18 1990-07-18 可変長符号化装置および可変長復号化装置

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EP0467678A2 EP0467678A2 (de) 1992-01-22
EP0467678A3 EP0467678A3 (en) 1992-10-14
EP0467678B1 true EP0467678B1 (de) 1997-04-02

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DE69125424D1 (de) 1997-05-07
US5304995A (en) 1994-04-19
EP0467678A3 (en) 1992-10-14
JPH0479421A (ja) 1992-03-12
DE69125424T2 (de) 1997-11-06
EP0467678A2 (de) 1992-01-22

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